In fields such as automobile lighting, it is becoming increasingly common to require power to be supplied at more than one voltage.
Consider as a non-limiting example an application in which lighting is required to be provided both by a string of several or many LEDs each of which have moderate brightness, as well as by a string of just a few LEDs each of which is a so-called “high brightness” LEDs.
Conventionally, the power to supply each string of LEDs, typically at a constant current, is provided by a respective buck converter. In applications such as automobile applications, the input supply voltage is typically lower than the maximum required voltage, and so a boost converter is included in order to increase the voltage to that needed. The output power from the boost converter, which provides the input power to the buck converters, must be at a voltage higher than the maximum required voltage—which is typically the voltage of the longest string of LEDs and including a small “overhead” allowance. The buck converter that drives the shortest string would then have to work at a very high current and low duty cycle. Operation at low duty cycle is generally difficult to effect at a high efficiency.